CAS simplification issues
12-16-2013, 03:23 PM
Post: #1
 Cristian Arezzini Member Posts: 72 Joined: Dec 2013
CAS simplification issues
This might just be a trivial mistake that I made in the setup.. but... look at this screenshot, taken in the CAS screen. The first two lines are OK, and behave as expected. But why isn't the third line simplified? On the 50g I get 3*a, which is what I expect.
Also, on the Prime, if I enter sqrt(3*a^2), I get -a*sqrt(3). On the 50g I get |a|*sqrt(3) which is more consistent with the math I learned in college.
So, what's happening? Is it a setting or a bug?

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12-16-2013, 04:24 PM (This post was last modified: 12-16-2013 04:28 PM by CR Haeger.)
Post: #2
 CR Haeger Member Posts: 275 Joined: Dec 2013
RE: CAS simplification issues
Try unchecking Use i: in CAS settings.

After this, setting Simplify: max will auto simplify this. I tend to leave Simplify at minimum.
12-16-2013, 09:57 PM
Post: #3
 Cristian Arezzini Member Posts: 72 Joined: Dec 2013
RE: CAS simplification issues
Uh... that worked, thanks... but what's the rationale behind that? I don't get it, since I don't think i is involved here... And why the minus sign in that result? Hm... If they don't want to display the absolute value, why negative and not positive?
12-16-2013, 10:40 PM (This post was last modified: 12-16-2013 10:46 PM by Mark Hardman.)
Post: #4
 Mark Hardman Senior Member Posts: 525 Joined: Dec 2013
RE: CAS simplification issues
(12-16-2013 03:23 PM)Cristian Arezzini Wrote:  Also, on the Prime, if I enter sqrt(3*a^2), I get -a*sqrt(3). On the 50g I get |a|*sqrt(3) which is more consistent with the math I learned in college.

With my CAS settings as:

Simplify: None
Exact
Use Sqrt
Principal

I get the results that you are looking for:

Mark Hardman

Ceci n'est pas une signature.
12-16-2013, 11:11 PM (This post was last modified: 12-16-2013 11:25 PM by Mark Hardman.)
Post: #5
 Mark Hardman Senior Member Posts: 525 Joined: Dec 2013
RE: CAS simplification issues
As to your first issue, I think that parisse has already agreed that there is a bug in NTHROOT in the latest Prime release of xcas (1.1.0-27). See the following thread in the old forum.

For now, he suggests using fractional exponents as a work-around.

Mark Hardman

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12-17-2013, 05:05 AM
Post: #6
 Cristian Arezzini Member Posts: 72 Joined: Dec 2013
RE: CAS simplification issues
OK, so removing the "use i" works for the square root. But the cubic root still doesn't work (the cubic root of a^3 still isn't simplified).
Entering it as (a^3)^1/3 works.

But I found another small bug/inconsistency on entering the exponents.
If I type a, then ^, then 3, I'm left with the cursor next to the exponent (3), ready to add something to it. If I press the right cursor key, the cursor leaves the exponent as expected, and moves down at the same level of a. If then I press ^ 1 / 3, to add the fractional exponent, I would expect the new exponent to refer to (a^3); instead it apparently still refers to just the 3. I think the expected behavior should be to refer it to the mathematical entity to its left, which is (a^3) and not 3. The parentheses could be automatically added or even just implied...
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